Split impellers, having an axial-flow rotor portion known as an inducer followed by a centrifugal rotor portion known as an exducer, typically have disc bodies attached together by a spigot arrangement to provide a frictional attachment. The intimate contact between discs results in high contact stresses between discs. Also, lack of axial spacing between discs means that inducer and exducer blade fillets are truncated, resulting in localized blade roots stresses. In some applications exducers may also have the blade leading edges extending axially upstream from the disc (i.e. the leading edge is overhung relative to the disc. All of these factors are detrimental to the stresses in the spigot configuration and particularly in the exducer leading edge region. Localized contact patterns on the contact surfaces of the spigot configuration result from local distortion of the disc bodies during engine transients (especially quick accelerations), which produces spigot load peaks, and results in high compressive stress both in the exducer blade leading edge root and at the contact points.
Accordingly, there is a need to provide an improved spigot arrangement for a split impeller for gas turbine engines.